Cooled ultrasonic transducer

ABSTRACT

Ultrasonic apparatus comprises a centrally bolted ultrasonic transducer having passages for internal cooling by a stream of fluid such as air. Radial ducts in a metal back mass open into an enlarged portion of a first bolt hole adjacent the bolt for supplying air. Air then flows forward through an annular passage in the piezoelectric crystal means and enters an enlarged portion of a second bolt hole in a metal front mass from which it is discharged through radial ducts in the front mass. Both enlarged portions should be of oval shape to assure strength and rigidity. A housing can surround the transducer for externally cooling it with a stream of air. The transducer can be mounted on the housing by a perforate plate or flange.

United States Patent Loveday 14 1 Sept. 26, 1972 COOLED ULTRASONIC TRANSDUCER 3,394,274 7/1968 Jacke et al. ..3l0/8.2 X [72] Inventor: Thomm E. Loveday, Rochester,

Primary Examiner-J. D. Miller *'"f'"""" Assistant Examiner-Mark O. Budd Asslgnee: Eastman Kodak Company Roch Attorney-William T. French, Robert F. Crocker and esters Henry M. Chapin App! l18797 Ultrasonic apparatus comprises a centrally bolted ultrasonic transducer having passages for internal cool- 52 US. Cl. ..310/8.9, 3l0/8.2, 310/8.7, g by a Stream of fluid Such as air Radial ducts in a 310/91, 310/26 metal back mass open into an enlarged portion of a 51 Int. Cl. ..n04|--17/00 first bolt hole adjacent the bolt for pp y Air [58] Field of Search ..3l0/8.2-8.9, 9.1, then flows forward through an annular passage in the 31()/9 4,26 piezoelectric crystal means and enters an enlarged portion of a second bolt hole in a metal front mass [55 Rgf mn e Cit d from which it is discharged through radial ducts in the front mass. Both enlarged portions should be of oval UNITED STATES PATENTS shape to assure strength and rigidity. A housing can 3 555 297 1/1971 Pierson ..310/8.3 surmund the transducer externally it with 2 831 295 4/1958 Weiss ..3 l0/8.2 x a The transducer can be mmmted 3:283:l82 11/1966 Jones et al. ..3 lO/8.7 husmg by a Perfmte Plate flange- 3,563,086 2/1971 Reed, Jr ..310/8.3 X 8 Chims, 3 Drawing Figures 3,495,104 2/1970 Burgo et al. ..3l0/8.3 X v v s PATENTEDSEP26 I972 3.694.675

THOMAS E LOVEDAY INVENTOR.

ATTORNEY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel ultrasonic transducer construction having provision for improved cooling of the vibration producing elements.

2. Description of the Prior Art Ultrasonic transducers have been well known for a number, of years and have found extensive applications in industry for the welding of plastics and the like. The most commonly used ultrasonic transducers depend upon piezoelectric crystals for generating the desired vibrations when oscillating electrical currents are applied thereto. An example of such an ultrasonic transducer is described in U.S. Pat. No. 3,328,610. When transducers are used continuously, the crystals tend to become quite hot and it has been found necessary to cool them as by passing a flow of air around the outside of the transducer. While this is effective, I have found that substantial heat still tends to build up in the crystals and the efficiency of cooling should be improved if possible.

U.S. Pat. No. 3,555,297, in the name of Charles W. Pierson, describes a novel cooled transducer wherein air is blown down through a central clamping bolt, up around the outside of the bolt, and then radially out ward through passages between the piezoelectric crystals and the adjoining metal parts, such as radially grooved front and backmasses and an intermediate metal spacer plate. This construction is excellent for its cooling effect, but suffers from the disadvantage that the surfaces of the crystals are not fully supported where the adjoining metal parts have grooves for the passage of air, thus subjecting the crystals to possible fracture when they are energized.

In U.S. Pat. No. 3,495,104 of RA. Burgo et al. an ultrasonic transducer is externally cooled by maintaining it within a surrounding pool of liquid such as oil. This construction is excellent for many operations, but is relative'lycomplex construction, and the possibility of an .oil leakv onto the work, or onto internal crystal surfaces, makes it undesirable for use' where oil'can damage such work as photographic film or paper. Moreover, there is no internal cooling of the transducer crystals.

SUMMARY OF THE INVENTION In accordance with the present invention the efficiency of cooling a centrally bolted ultrasonic transducer is improved by providing for the flow of cooling fluid, such as air, through passage means in a metal back mass to the interior of the transducer, and then forward through the interior in contact with the piezoelectric crystals to the front mass, from which the airis discharged to the outside through second passage means.

With this construction the piezoelectric crystal discs are fully supported over their entire flat surfaces by adjoining metal parts.

Provision is' also made for externally cooling the transducer by surrounding it with a cylindrical housing to which the transducer is connected by a perforate support which is clamped between elements of the transducer. Air is introduced into the housing and flows over the outside of the transducer and out through perforations in the support.

THE DRAWING FIG. 1 is a vertical sectional view through a transducer apparatus embodying the novel cooling construction of the present invention;

FIG. 2 is a cross sectional view taken along the line 2-2 in FIG. 1; and

FIG. 3 is a cross sectional view taken along the line 3-3 in FIG; 1.

THE PREFERRED EMBODIMENT propriate function, such as splicing.

A central retaining bolt 19 extends through axially aligned bolt holes 20 and 21 in the masses 11 and 13, respectively, and in the crystal means C, and is threaded at its end into the front mass 13. The head of bolt 19 bears against the top of back mass 1 l to hold all elements tightly together. I The crystal means C comprises upper and lower piezoelectric crystals discs 23 and 25, and an intermediate electrically conductive metal spacer disc 27 to which conductor 28 is secured. Spacer 27 has opposite faces in intimate contact with the faces of the crystal discs, all three elements being annularly spaced from bolt 19 so that no electrical contact is made with the bolt. Insulation from the bolt can additionally be assured by positioning a cylindrical insulator (not shown) within the annular space 33, with a sufficiently loose fit to permit the flow of air. Discs 23 and 25 can be any desired piezoelectric crystal material, but the well known PZT crystal (lead-zirconate-titanate) is preferred.

Bolt hole 20 is a cylindrical bore in its upper portion to fit tightly with the shank of bolt 19. A lower portion of bolt hole 20 is enlarged on opposite sides thereof at 22 and 24, thus having a generally oval cross sectional shape, to provide passages for cooling fluid. The wall at the minor axis of the oval engages the bolt 19, while the wall at the major axis is spaced from the bolt. Two oppositely extending radial bores or ducts 37 and 39 extend transversely from passages 22 and 24 to the outside of the transducer where they are connected to a pair of air supply conduits 41 and 43. Bolt hole 21 in front mass. 13 is threaded for engagement with the threads of bolt 19, and also has enlargements 45 and 46 which are angularly displaced from 22 and 24, and which give the upper portion of the bolt hole a generally oval cross sectional shape with its walls and the threads at the minor axis engaging the threads of bolt 19, and with the walls at the ends of the major axis spaced from the bolt. The remainder of bolt hole 21, between the enlargements, retains its threads which engage the bolt 19. Two radial ducts 47 and 49 extend transversely from passages 45 and 46 to the outside of the from mass and are positioned at 90 to the ducts 37 and 39.

It is thus seen that the construction and arrangement is such that continuous passage means for conducting cooling fluid through the interior of the transducer is formed, comprising the radial passage means, the axially aligned bolt holes, and the central holes in crystal means C. Thus, adequate cooling is provided during operation while avoiding both the problem of potentially inadequate crystal support, and the possibility of oil leaks. Instead of using oval shapes, cylindrical counterbores can be used. However, the oval shapes provide certain important advantages. For example, the oval shape of portions of bolt holes 20 and 21 provides for rigidity and better support of all transducer elements, with less possibility of flexing and distortion, than when cylindrical counterbores are provided. A cylindrical counterbore in the front mass also would leave a longer length of the bolt free from contact with the interior,

thus affecting the resonant frequency and performance adversely.

The structure described above is advantageous regardless of how the transducer is supported. However, generally the transducer is supported by an external cylindrical housing 51 which surrounds the transducer T in annularly spaced relation thereto, and is connected thereto by a transversely extending support plate 53 constituting a part of front mass 13. Plate 53 has perforations 54 for the passage of fluid out of housing 51 and for interrupting the transmission of vibrations from the transducer to the cylindrical housing. Plate 53 is shown as a separate metal flange which is clamped between one end of crystal disc 25 and the rest of front mass 13, but it can also constitute an integral part of a unitary front mass. Plate 53 has a central aperture 55 therein to permit air to flow into passages 45 and 46. At its periphery, plate 53 is bolted or otherwise secured to housing 51. Cooling air is introduced into housing 51 through an inlet 57 and flows over the outside of the transducer and out through the apertures 54 in support plate 53.

It should be noted that the radial discharge passages 47 and 49 in the front mass 13 are located on the outside of housing 51, spaced from plate 53, so as to avoid mixing of the heated air from the interior of the transducer with the air circulating over the outside of the transducer.

The simple construction described in detail above effectively cools an ultrasonic transducer which is being used continuously for splicing or sealing plastic materials, and avoids the drawbacks of the prior art such as potential oil leakage, and potential breakage of inadequately supported crystals. My transducer at low power runs about 30 percent cooler than a transducer having no internal cooling. Moreover it is capable of operating continuously at 150 watts input for periods as long as 2 hours.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. Ultrasonic apparatus comprising an ultrasonic transducer comprising, in combination,

a metal back mass having a first longitudinal bolt hole;

a metal front mass having a second longitudinal bolt hole aligned with said first bolt hole;

annular piezoelectric responsive means sandwiched between said front and back masses, and having 4 central passagemeans therethrough aligned with said first and second bolt holesyand a central retaining bolt passing through said first bolt hole, through said central passage means in spaced relation to the wall thereof, and into said second bolt hole;

said first and second bolt holes being enlarged transversely over only portions thereof adjacent said piezoelectric responsive means to space the walls thereof from said bolt;

and said back mass and said front mass having first and second passage means therein, respectively, extending transversely from the outside thereof into the enlarged portions of the bolt holes therein, the construction and arrangement being such that continuous passage means for cooling fluid is formed comprising said transverse passage means, said enlarged portions, and said central passage means; said apparatus also comprisinga housing surrounding said transducer in annularly spaced relation thereto, and conduit means extending between the inside and the outside of said housing and connected into said first passage means in said back mass for supplying cooling fluid thereto.

2. Ultrasonic apparatus in accordance with claim 1, said first and second passage means being a plurality of radial passages in each of said back and front masses.

3. Ultrasonic apparatus in accordance with claim 2, each of said back and front masses having two of said radial passages aligned axially with one another, the passages of said back mass being displaced from those of said front mass.

4. Ultrasonic apparatus in accordance with claim 1, each of said first and second bolt holes comprising portions of generally oval cross section at the ends thereof toward said crystal means, and portions of cylindrical cross section at the ends thereof away from said crystal means, the walls of said cylindrical portions and the walls at the ends of the minor axes of said oval portions engaging said bolt, the walls at the ends of the major axes of said oval portions being spaced from said bolt, said first and second passage means opening into said bolt holes at the ends of said major axes.

5. Ultrasonic apparatus in accordance with claim 4, the major axes of said oval portions being displaced 90 from one another.

6. Ultrasonic apparatus in accordance with claim 1, also comprising a perforate supporting device connecting said transducer to said housing, and means for introducing cooling fluid into said housing to flow around the outside of said transducer and out through the perforations in said supporting device, said second passage means being located outside of said housing and spaced from said supporting device.

7. Ultrasonic apparatus in accordance with claim 7, said supporting device being a metal flange clamped against said piezoelectric responsive means, said flange having a central bore provided with a wall spaced annularly from said bolt and aligned with said central passage means, and with said bolt holes.

8. Ultrasonic apparatus in accordance with claim 1, said first passage means being a plurality of individual radial passages in said back mass, said conduit means comprises a plurality of individual conduits severally extending from said radial passages between the inside and the outside of said housing.

' I UNHE D STATES EATENT OFFICE CERNHCATE @l? QQRREQHON Patnt No. 359M575 Dated September .1972 Inv ntofls) T o s Lcveday I l It is certified that erro r appears in the above-idextified patent I and that said Letters Patent are hereby corrected asshown below: r.

Column A, line 57; claim 7" should read" "claim 6--.

Signed and sealed this 15th day of My 1973.

SEAL) Attest:

EDWARD 'M.FLETCHER,JR; 3 ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents (5/69) "UNITED STATES PATENT OFFHIE smmwmrs or asssmios Patent No. -7 Dated Septeamb'er 1972 Inventor) Thomas E. Loveday It is certified that error appears in the above-identified petent and that said Letters Patent are hereby corrected as shown below: 7

Column L, line 57, "claim 7" should read" --claim 6--.

Signed and sealed this 15th day of May 1973.

(SEAL) Attest:

EQVQARD M.FLETHER JR ROBERT GOTTSCHALK A estlng Offlcer' Commissioner of Patents 

1. Ultrasonic apparatus comprising an ultrasonic transducer comprising, in combination, a metal back mass having a first longitudinal bolt hole; a metal front mass having a second longitudinal bolt hole aligned with said first bolt hole; annular piezoelectric responsive means sandwiched between said front and back masses, and having central passage means therethrough aligned with said first and second bolt holes; and a central retaining bolt passing through said first bolt hole, through said central passage means in spaced relation to the wall thereof, and into said second bolt hole; said first and second bolt holes being enlarged transversely over only portions thereof adjacent said piezoelectric responsive means to space the walls thereof from said bolt; and said back mass and said front mass having first and second passage means therein, respectively, extending transversely from the outside thereof into the enlarged portions of the bolt holes therein, the construction and arrangement being such that continuous passage means for cooling fluid is formed comprising said transverse passage means, said enlarged portions, and said central passage means; said apparatus also comprising a housing surrounding saiD transducer in annularly spaced relation thereto, and conduit means extending between the inside and the outside of said housing and connected into said first passage means in said back mass for supplying cooling fluid thereto.
 2. Ultrasonic apparatus in accordance with claim 1, said first and second passage means being a plurality of radial passages in each of said back and front masses.
 3. Ultrasonic apparatus in accordance with claim 2, each of said back and front masses having two of said radial passages aligned axially with one another, the passages of said back mass being displaced 90* from those of said front mass.
 4. Ultrasonic apparatus in accordance with claim 1, each of said first and second bolt holes comprising portions of generally oval cross section at the ends thereof toward said crystal means, and portions of cylindrical cross section at the ends thereof away from said crystal means, the walls of said cylindrical portions and the walls at the ends of the minor axes of said oval portions engaging said bolt, the walls at the ends of the major axes of said oval portions being spaced from said bolt, said first and second passage means opening into said bolt holes at the ends of said major axes.
 5. Ultrasonic apparatus in accordance with claim 4, the major axes of said oval portions being displaced 90* from one another.
 6. Ultrasonic apparatus in accordance with claim 1, also comprising a perforate supporting device connecting said transducer to said housing, and means for introducing cooling fluid into said housing to flow around the outside of said transducer and out through the perforations in said supporting device, said second passage means being located outside of said housing and spaced from said supporting device.
 7. Ultrasonic apparatus in accordance with claim 7, said supporting device being a metal flange clamped against said piezoelectric responsive means, said flange having a central bore provided with a wall spaced annularly from said bolt and aligned with said central passage means, and with said bolt holes.
 8. Ultrasonic apparatus in accordance with claim 1, said first passage means being a plurality of individual radial passages in said back mass, said conduit means comprises a plurality of individual conduits severally extending from said radial passages between the inside and the outside of said housing. 